This invention relates to dentistry, and more particularly to a two-part dowel pin for prosthodontic casts, as well as tools for use therewith.
In making models of a patient's teeth, it is common practice to first form a negative impression of the teeth. Dowel pins are positioned in the center of the impressions of particular teeth which are to be worked on. The negative impressions of the teeth are then filed with a die material to form a positive replica or die of the teeth.
In the formation of such dental models, the dental model cast is situated on a base cast. The dowel pins are utilized for positioning the dental model cast on the base cast. Numerous manipulations take place on the dental model cast and it is accordingly required to frequently insert and remove the dental model cast from the base cast.
In the prior art, it was common practice to utilize one piece dental pins. Such pins had numerous shapes and arrangements. For example, in applicant's own U.S. Pat. Nos. 3,875,665 and 3,932,939, dowel pins are disclosed of such one piece construction. In the latter patent, two pins are utilized, one as a locating pin and one as an aligning pin between the dental model cast and the base cast. Other shapes of dowel pins are described in U.S. Pat. No. 3,286,385 where the dowel pin is utilized in conjunction with a clip inserted in the base cast which provides a spring-like retention on the dowel pin. A pin and sleeve combination is described in U.S. Pat. No. 3,518,761 to facilitate insertion and removal of the dowel pin from a sleeve which is inserted in the base cast. A further shaped dowel pin is described in U.S. Pat. No. 1,279,805.
All of these, however, utilize a one piece construction which presents problems in the insertion and removal thereof. Frequently, the pin can become bent or damaged during continuous utilization and appropriate positioning of the dental model cast on the base cast become displaced.
In the aforementioned parent application, there is described a two part dowel pin for removably mounting a dental model cast relative to the base cast. The dowel pin includes a head portion and a shank portion extending therefrom. The head portion is adapted to be fixedly secured into the dental model cast so that the exposed end thereof is flush with a flat surface of the dental model cast. The shank portion is adapted to be removably inserted into a complementary opening provided in the base cast. Preferably, a sleeve member is provided in the opening to slidably receive the shank portion therein. Threads are provided on a male member extending from the shank portion which are received in a correspondingly threaded female portion formed within the head portion.
In the aforementioned parent application, the shank portion is provided with a vertical flat surface longitudinally extending from the free end thereof opposite the end of the shank portion having the threaded member. The vertical flat surface extends outwardly from the base cast and is engaged by a tool for rotating the shank to disengage the shank portion from the head portion. An undercut beneath the flat surface is available for insertion of a fork-like member to extract the shank portion from the base cast.
The two part dowel pin provides numerous benefits as were described in the aforementioned parent application. Specifically, it permits improved positioning, it provides for utilization of the dental model cast without interference by the cast and provides improved engagement between the two parts of the cast.
However, frequently the dental model cast must be manipulated and worked on while it is firmly held in place. Accordingly, it would be desirous to have the dental model cast able to be inserted into the base cast while it is being manipulated and worked on, and at the same time avoid the necessity of having a one-piece dowel pin which may have a tendency of becoming bent and damaged during continued insertion and removal from the base cast. Furthermore, the extension of the shank portion outwardly from the bottom of the base cast also may provide difficulty since it may be awkward to place the base cast on a surface and the exposed portions of the shank may also become bent or damaged.